This invention relates to a photosensitive resin composition and a photosensitive element using the same which are excellent in light-transmitting properties and solubility, can be made into a final cured film having excellent heat resistance, adhesive properties, flexibility, electrical properties and mechanical properties by heat treatment, can be formed into a thick film, have a high photosensitivity also when used in the form of a thick film, and are suitable for use in interlaminar insulating films or surface protective films of multilayer circuit board or semiconductor element, pastes for color filter, etc.
Heat-resistant polymers represented by polyimides are excellent in heat resistance, electrical properties and mechanical properties and hence have heretofore been used in interlaminar insulating films or surface protective films (e.g. .alpha.-ray shielding film, passivation film, buffer coat film, etc.) in semiconductor element. They have been widely used also in the field of circuit boards, for example, in resists for forming a circuit pattern on a substrate, or interlaminar insulating films of multilayer circuit board.
In the semiconductor industry, inorganic materials have heretofore been used in interlaminar insulating films and surface protective films, but in recent years, organic materials excellent in heat resistance, such as polyimides, have been used by taking advantage of their characteristics.
A pattern of a surface protective film or interlaminar insulating film of a semiconductor element or multilayer circuit board is formed through troublesome and various steps such as formation of a resist material into a film on the surface of a substrate, exposure of a predetermined portion to light, removal of an unnecessary portion by etching and the like, cleaning of the substrate surface, etc. Therefore, it is desirable to develope a heat-resistant photosensitive material which is such that after forming a pattern by exposure and development, a resist material in a necessary portion can be remained and used as it is as an insulating material.
As such a material, there have been proposed, for example, heat-resistant photosensitive materials obtained by using a photosensitive polyimide, a cyclized polybutadiene or the like as a base polymer. Photosensitive polyimides are particularly noted because of, for example, their excellent heat resistance and easy removal of their impurities.
As such a polyimide, for example, Japanese Patent Publication No. 49-17374 has proposed a system comprising a polyimide precursor and a dichromate, at first. But although this material is advantageous in that it has a practical photosensitivity and a high film-forming ability, it is disadvantageous, for example, in that it is poor in storage stability and that chromium ions remain in polyimide. Therefore, it has not been put into practical use.
Japanese Patent Publication No. 55-100143 and Japanese Patent Appln. Kokai (Laid-Open) No. 60-100143 have proposed processes in which a photosensitive group is given by using an ester linkage or an isocyanate compound, respectively. But the material obtained by the former process has low adhesive properties to a substrate and hence tends to be peeled off, while the material obtained by the latter process has low light-transmitting properties and is difficult to form into a thick film.